Demi Lovato -- who's struggled with an eating disorder for years -- says Lady Gaga's puking stunt at SXSW was despicable because it glamorizes a terrible disease in the name of art.
Lovato just laid a thick amount of shame on Gaga via Twitter ... saying "Sad ... As if we didn't have enough people glamorizing eat [sic] disorders already."
Demi adds, "Putting the word ART in it isn't a free card to do whatever you want without consequences."
One Twitter user quipped back ... Gaga has struggled with an eating disorder herself and spoke about it before the performance ... but Demi insists that doesn't give her a pass.
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